The invention relates to a medical instrument for the treatment of tissue by means of high-frequency current, comprising at least one electrode which can be supplied with high-frequency current and is arranged at a distal end of an elongate electrode carrier.
The invention also relates to a medical system comprising a medical instrument of this type.
An instrument of the type mentioned at the outset is known from WO 00/53079.
An instrument of the type mentioned at the outset is used in high-frequency surgery. High-frequency surgery is used therapeutically in various specialized medical disciplines such as, for example, urology, gynaecology, neurosurgery, abdominal surgery, etc. Specifically in urology and gynaecology, prostatic tissue or endometrial tissue is removed endoscopically by means of an instrument mentioned at the outset, which is also referred to as a resectoscope. The endoscopic HF-aided prostatic resection of benignly enlarged prostates is one of the most common endoscopic therapies. By means of the electrode which can be subjected to high-frequency current, which may be of a monopolar or bipolar design, in the latter case with two electrodes formed as opposite poles being provided, tissue is removed and/or coagulated and/or vaporized under the thermal effect of the high-frequency current. The at least one electrode is, for example, designed in the form of a loop and is therefore often also referred to as a loop or HF loop.
Currently, HF-surgical interventions by means of an instrument of the type mentioned at the outset, for example in the case of prostatic resection or resection of tumours in the thin-walled urinary bladder, are visually monitored endoscopically. For this purpose, the instrument is conventionally coupled to an endoscope optical system. Visual monitoring of the therapeutic intervention is inadequate however. In particular, the setting of the cutting depth of the electrode cannot be visually observed or projected as an image by endoscopic means. If cutting goes too deep, lesions occur to uninvolved tissue, for example of the prostate capsule in the case of prostate resection. Monitoring the depth of penetration of the electrode in the tissue could in principle be made possible by the use of image generating and, specifically, sectional-image generating methods such as ultrasound, X-ray, computer tomography or magnetic resonance. Navigating and locating systems of this type are already known for surgery or endoscopy. A basic prerequisite for navigation by means of such ultrasound, computer-tomography, magnetic-resonance or other image information is, however, the positional or orientational determination of the instrument with respect to a spatial reference, for example in such a way that the position of the instrument can be coupled positionally correctly into the image.
However, positional and/or orientational determination by means of ultrasound or infrared is unsuitable for sensing a position of an instrument in the body, since for such systems there is no visual contact with the location to be determined of the instrument in the body. Another possibility is a direct mechanical coupling of the instrument via position encoders to outside the body, which however is very disadvantageous on account of the great overall space required from outside the body to inside the body.
The document U.S. Pat. No. 5,273,025 discloses a device with which the position and orientation of a portion of a flexible shaft of an endoscope inserted into the body can be determined electromagnetically. For this purpose, arranged in the flexible shaft of the endoscope are one or more coils, which are excited by an electromagnetic field which is generated outside the body and coupled into the body through the surface of the body. The voltage which is induced in the coils by the external electromagnetic field and the intensity of which depends on the orientation of the coils in relation to the electromagnetic field is carried via a line through the shaft of the endoscope to an evaluating device outside the body and evaluated for the positional and orientational determination.
A further system for the electromagnetic determination of the spatial position and/or orientation of one or more objects is disclosed by EP 1 096 268 A2. This known system uses a coil which is excited by an electromagnetic field generated outside the body and which is fastened on the object of which the position and/or orientation is to be determined. The object of which the position or orientation is to be determined is in that case a flexible element, which can, for example, be inserted into a catheter.